Some applications and apparatuses may require measuring a volumetric fluid flow rate through a fluid passage, such as a conduit or duct. For example, in a rooftop HVAC system, it is often desirable to know the volumetric airflow that the rooftop HVAC system brings into a building in real time. One example of an airflow monitoring system for a HVAC system is the Traq™ airflow monitoring system manufactured by the Trane Company (LaCross, Wis., U.S.A.). The Traq™ airflow monitoring system typically includes an airflow sensor, such as described in U.S. Pat. No. 4,344,330, in an airflow modulation device, such as described in U.S. Pat. Nos. 5,741,180 and 5,674,125. In each Traq™ airflow monitoring system, the airflow sensor can measure the volumetric airflow through the airflow modulation device. An air intake conduit of the HVAC system may be equipped with one or more Traq™ airflow monitoring systems, so that essentially the entire air intake by the HVAC system may go through the Traq™ airflow monitoring system(s). The total volumetric air intake flow then can be calculated by adding the volumetric airflow values measured by individual Traq™ airflow monitoring system.